Discharge lamp system



Nov. 1, 1938; E; F. w. ALEXANDERSON 2,135,268

DISCHARGE LAMP SYSTEM Filed March 27, 1937 Ernst F: W Alexanderson,

51AM! by l i fi zAttor hey;

Patented Nov. 1, 19 38v UNITED STATES PATENT OFFICE v 2.13am v DISCHARGE LAMP BYS'L'EM Ernst, n,- w. Alexanderaon, Schenectady, N. 1n, usignor to General Electric Company, a corporation of New York Application w th 21, 1937, Serial No. 133,441

\ scum. '(Ol. 110-124i My invention will be better understood from the following description taken in connection with the 10 accompanying drawing, and its scope will be pointed out in the appended claims.

Referring to the drawing, thesingle figure of which is a circuit diagram illustrating an embodiment of my invention, I have shown the dis- 15 charge lamp I as a gas discharge cold cathode lamp of the small high pressure mercury vapor type such as that disclosed and claimed in the copending application of Cornelis 301 et 131., Serial No. 46,952,;filed October 26, 1935 and assigned to 20 the same assignee as the present application. The lamp l is shown connected to be opera-ted; from the 60 cycle, 110 volt lighting circuit 2. In-

asmuch as the lamp requires a higher voltage than that ofltlie circuit 2 for its operatiom'for V 25 example 440 volts, I have shown it connected with' the source of supply through the step-up transformer 3. a

It is well known that when such a discharge lamp is connected across a source oi' supply of K 9 alternating current of proper voltage there will be as many light flashes per second as there are alternations of the current. In other words, the frequency of the light flashes will'be equal to twice the frequency of the alternating current 35 in cycles per second. In accordance with my invention now to be described thenumber of flashes to be produced by the lamp will be one-half the number of alternations; hence it will equal the frequency of the alternating current in cycles per 40 second. This result I obtain by modulating the wave form of the voltagesupplled to the lamp whereby each half cycle of supply voltage of one polarity causes the lamp to emit light while each half cycle of the opposite polarity does not 45 cause the lamp to emit light but is sumcient only to maintain the ionization in the lamp produced by the previous half cycle. I eilectsuch. modification of the wave form by inserting in the lamp ci cuit means which offers a low resistance to 543 the flow of current in one direction whereby the lamp becomes illuminated but which ofiers a high resistance to the flow of current in the opposite direction, the voltage supplied to the lamp at that being only suflicient to maintain the lamp in 55 its ionized condition. For this purpose I have shown in the drawing the rectifier 4 connected in series with the lamp and the transformer secondary and have shown the rectifier shunted by the resistor 5. The resistance of the resistor 5 is of such a value that during that half cycle at which 5 the rectifier normally prevents the fiow of current through the lamp only sufficient voltage is supplied to the lamp as is necessary to maintain the lamp in its previously ionized condition. Such a resistor may, for example, have a resistance of the order of 5,000 to 10,000 olugs.

Insteadof employing a recti er having a resistor connected in shunt therewith as shown by the drawing, I may employ a rectifier whose resistance to the flow of current in the reverse direction or direction normally prevented by the rectifier is of the order of that provided by the resistor 6. In that case one may dispense with a separate resistor as the rectifier itself will naturally pass sufiicient current in the reverse direction to supply the necessary voltage to the lamp for maint ionization therein until the next half cycle occurs.

Inasmuch as a lamp such as I have described requires a voltage to produce a discharge therein which is very much higher when the lamp is hot than when it is cold, it will be'seen that by maintaininga condition of ionization in the lamp during the lion-luminous half cycles, the lamp can be successfully operated from a source of volt- 7 age sumcient only to start the lamp from acold condition. Inasmuch as the voltage for maintaining ionization lathe lamp may be limited to that required for the ionization without being sufiicient to cause the lampto give any light or at least any appreciable light during the nonluminous half cycles, the light fiashes' produced by the lampcorrespond in number to the frequency of the alternating current supply.

. My invention is adapted for various uses. One use, by way of example, is in a motion picture projector wherein the discharge lamp provides the source of light for the projection. In this case the usual shutter may be dispensed with provided the number of pictures projected per second is equal to one half the frequency of the alternating current supply. For example, if a 60 cycle alternating current is employed the shutter may be omitted ii the intermittent mechanism of the projector is operated at such a speed or is so constructed that 30 pictures per second are projected. It is of course necessary to time the light flashes so that they occur only during these periods in which the film is stationary; -Ohviously each picture then will be projected twice, g

once for each flash, the two projections serving the same purpose of avoiding the sensation o! flicker as does the usual flicker shutter.

Another use of my invention is that of a source of illumination for taking motion pictures. During those periods at which the camera shutter is closed there is no need or having the subject illuminated or at least illuminated to the extent necessary for the proper exposure. One may therefore economize on the production oi light by employing a system such as I have disclosed herein and operating the camera shutter in synchronism with the light flashes. Ii a cycle current is employed and the camera makes 30 exposures per second the timing of the shutter should be such that alternate flashes come during the closed periods of the shutter thereby to avoid double exposures. I prefer, however, in this case to employ a lower frequency current, for example, a current of 24 cycles per'second and to operate the camera at the usual speed to take the standard number or 24 pictures per second. All the light flashes then will be made to occur during the exposure periods of the camera and a maximum economy will be effected.

I have chosen the particular embodiment described above as illustrative of my invention and it will be apparent that various modifications may be made without departing from the spirit and scope or my invention which modifications I aim tocover by the appendedrclaims.

What I claim as new and desire to secure by Letters Patent 0! the United States is:

1. In combination, a high pressure mercury vapor discharge lamp having a high operating temperature, means for supplying thereto an alternating voltage sufllcient .to cause the lamp to start ata non-operating temperature but insuifl cient to cause it to start when deionized and at its operating temperature, and means connected in circuit with said lamp for limiting alternate half cycles of the supply voltage to a value sufllcient to maintain the lamp ionized without causing it to emit an appreciable amount of light.

7 2. In combination, a high pressure mercury vapor discharge lamp having a high operating temperature, means for supplying. thereto an alternating voltage suflicient to cause the lamp to start at a non-operating temperature but ins sufllcient to cause it to start when deionized at its operating temperature, a rectifler connected in series with said lampfor interrupting the voltage supply thereto during alternate half cycles and a resistance in shunt with said rectlfler for by-passlng sufiicient voltage to the lamp during Q 25.

each of said half cycles to maintain the ionization in the lamp until the following hali cycle without the production of an appreciable amount of light.

ERNST F. w. ALEXANDERSON. 

